This invention relates to ball valves and more particularly to improvements to ball valves to allow the valves to operate more effectively over longer periods of time without leakage.
In refining operations, in a moving bed catalytic reformer, a bed of catalyst is moved in batches through vessels and communicating conduits which employ valves for flow control purposes. Hydrogen pressure of the order of 150 psi is employed for transferring the catalyst through the conduits and hence through the valves. For successful operation of the process, the valves must hold hydrogen pressure without leakage. Due to the small size of the hydrogen molecules, difficulties have been experienced in finding a suitable valve which will hold the hydrogen pressure without leakage after repeated use.
One type of valve which has been tried is a ball valve which comprises a valve body having a ball receiving cavity with aligned inlet and outlet passages leading to the cavity. A stainless steel ball with an opening formed therethrough is rotatably supported in the cavity between the inlet and outlet passages. Means is provided for rotating the ball to an open position wherein its opening is aligned with the inlet and outlet passages and to a closed position wherein its opening is out of alignment with the inlet and outlet passages. Sealing is accomplished by two ring-shaped seats located in the valve body on opposite sides of the cavity for engagement with the ball and which define a portion of the inlet and outlet passages respectively. These seats each comprise a seating material, supported in a metal ring, and which has a seating surface for engagement with the ball. The seating material also engages the valve body on the back side of the ring. The seating material may be of carbon-graphite or Teflon or it may be formed of Armco iron, which is virtually pure iron, or of McCannalloy 88, which is a nickel-base alloy.
Ball valves of this type have been tried in a catalyst transfer system, however, it has been found that they leak soon after installation requiring the complete catalyst transfer system to be shut down.